Background and Purpose: Acute appendicitis is common in clinical acute abdominal pain. Typical cases are easy to diagnose, but sometimes it can be very difficult to make a diagnosis of atypical cases. Therefore, the retrospective study aims to evaluate the diagnostic accuracy of ultrasound in patients rightsided lower abdominal pain suspected to have acute appendicitis. Subjects and Methods: Subjects included 127 patients (58 male and 69 female) aged between 6-89 years of age (mean: 34.8 years). From the results of the ultrasound, appendicitis is classified as follows: 1) catarrhal: a clear layer structure of the appendiceal wall and mucosal edema
2) phlegmonous: an ill- defined layer structure of the appendiceal wall, moderate enlargement of the apendix, and maximum transverse dimension of or = 10 mm
and 3) gangrenous: unidentifiable layer structure of the appendiceal wall and marked enlargement to form a mass. Results: Ultrasound see appendix 127 of 158 patients with clinical signs of appendicitis (80.4 percent). In the case that this is appendicitis, ultrasound sensitivity was 96.7 percent, specificity 89.1 percent, and 93.7 percent accuracy. In 31 patients ultrasound did not show appendicitis, with 6 cases (19.3 percent) were clinically diagnosed as appendicitis and surgery. Assess the severity of inflammation, ultrasound and pathology consistent with the 59.8 percent of cases. The rest, ultrasound often underestimate the degree of inflammation of the appendix, the ultrasound should therefore be considered when distinguishing between levels of catarrhal or or phlegmonous appendicitis, it is important to make a decision to surgical treatment.